When did dark heresy come out?

I'm curious, could you tell me when the game known as Dark Heresy was first released? I've heard quite a bit about its unique blend of dark fantasy and role-playing elements, and I'm interested in knowing more about its history and origins. I understand that it's part of the Warhammer 40,000 universe, but I'm specifically interested in the timing of its initial launch. Could you provide me with a specific date or year?